Today’s planning standards deal with extreme situations in distribution network operations – possible reserves, due to considering stochastic approaches, are not yet used. The grid is designed and sized for contingencies of few hours or days per year. New methods for operational planning at distribution level and active operation of low voltage networks can reduce the high costs associated with upgrading power distribution infrastructure to host the expected additional generation and load. The Austrian project DG Demonet Smart LV grid addresses this challenge and focuses on making available new network management possibilities while taking into account the deployment of Automatic Meter Reading (AMR) in many places.
The main challenge regarding the integration of DER in distribution networks is to keep the voltage within the specified limits (voltage band, in compliance with EN 50160 “Voltage characteristics of electricity supplied by public distribution systems”). Thus, the main functions elaborated in the field tests are:
1. Intelligent planning (resulting in new planning methods enabling higher DER densities)
3. Active management and control
using communication infrastructures
at LV level restricted in bandwidth and availability (resulting in new and cost-effective active low voltage network control solution approach enabling higher DER densities).
These concepts will be validated in a proof of concept in real LV network sections. This validation will also provide new insights for future business models for feed-in into low voltage networks.
One of the major technical foundations for this project was laid with the newly developed method “Power Snap-Shot” (PSS). Smart meters have been adapted in order to capture an instantaneous image of the network, taking into account the simultaneous display of measurements (voltage level, effective and reactive load) caused by a trigger state. By analysing the obtained measurement data of up to 50 different low voltage networks (including urban and rural structures), the potential for implementing a smart grid approach for an active network operation in low voltage networks can be evaluated for the first time. Results from this analysis contribute to investigating and to modelling low voltage networks more precisely, which leads to an essential improvement of network planning and network operation in distribution networks.
Beside the definition and demonstration of new intelligent network planning approaches (probabilistic based network interconnection requirements), two main test cases have been implemented:
- Active network operation and voltage control with a high share of PV (Eberstalzell and Littring)
- Active network operation and voltage control with a high share of PV and e-mobilty (Köstendorf)
Test Case 1 Active network operation and voltage control with a high share of PV – installations (Köstendorf and Littring): At the demo site in Eberstalzell, increased hosting capacity for rooftop PV installations is made possible by local autonomous voltage level control at on-load tap changer in the secondary substation, using real time measurement of voltage from smart meters transmitted by PLC. In addition, reactive power from inverters reduces the voltage spread and is coordinated by a control unit at the secondary substation. Thus PV-plants can evolve from “Troublemakers” to “Troubleshooters” and an increased penetration of DG is conceivable. In Eberstallzell and Littring every second house was equipped with PV unit (Eberstalzell: 30/0,4 kV – 630 kVA Transformer, 11 branches up to 600m, 165 Buildings/Customers - 173 customers, 1.3 GWh/a 450 kW maximum load, 60 PV-Systems roof top 330kWp; Littring: 30/0,4 kV – 250 kVA Transformer, 5 branches up to 1 km, 54 Buildings/Customers, 15 farmers, 8 households, 1 small saw mill, 1 fish farm, 0.35 GWh/a 120 kW maximum load, 15 PV-Systems roof top 140 kWp).
Figure 1: Control and Communications Concept Eberstalzell and Littring
Test Case 2: Active network operation and voltage control with a high share of PV installations and e-mobilty (Köstendorf): In the Köstendorf test case, integration of EVs is additionally addressed. A high penetration of e-mobility in LV networks is demonstrated. In practice, each customer who installed a PV system within the project framework is also equipped with an electric car for at least a one year period. The customers are interconnected with broad band communication lines which are used in parallel for television and internet. Each charging unit, as well as upcoming further devices, is controlled by a Building Energy Agent unit. The real-time voltage measurements and the transfer of related data are realized by smart meters. Main parts of the voltage-var-control are implemented in a central system and are interconnected via the Energy Information Network which also enables control of the reactive power of PV Inverters. Almost every second house was equipped with PV and e-mobility (191,4 kWp installed generation capacity by 43 PV-Systems, 36 e-cars with a maximum power consumption of about 133 kW, 95 buildings / 127 customers, 210 kW maximum load without e-mobility, Transformer station 30/0,4 kV in Köstendorf)
Figure 2: Control and Communications Concept Köstendorf
A specific work package of the project is dedicated to legal and economic analyses, including cost /benefit analyses. A new approach for the general assessment of distributed generation units will be developed, taking into consideration the statistic behaviour of different influencing parameters and the probability of 100% generation as well as the simultaneity of different energy resources. In addition, the overall best out of network costs and energy yield is determined. An approach for DG assessment with probabilistic network analyses and related legal framework and business model will be developed.
Furthermore a legal and economic evaluation of the specific grid control and integration concepts of DER is carried out in the project. Adequate business models for utilizing generators and loads as control strategy actors are developed, providing the right incentives towards actors’ participation. Furthermore, Austrian legal framework conditions are analysed besides the economics of each control strategy. Finally, corresponding recommendations will be provided.
The solutions for field testing have to be installed and operated in consultation with the relevant network customers. Moreover, some substantial inputs for potential business models may derive from the interaction with the customers and their feedback. Finally, the project will provide technically, economically and legally evaluated voltage control concepts and network planning approaches in order to increase the hosting capacity for distributed energy resources (DER) and e-mobility of low voltage distribution networks.
For more information, please visit http://www.smartgridssalzburg.at/forschungsfelder/stromnetze/smart-low-voltage-grid/ (website only available in German)